Ann Taylor sandbox 114

Mechanism of Trypsin-2AGE Mutant Andrew Alexander, Justin Allen, Mike Lu
The mechanism of trypsin is a serine protease reaction which utilizes a catalytic triad made of histidine-57, aspartate-102, and serine-195. These are the active sites where the reaction occurs by modifying the environment of the serine. It also contains an oxyanion hole that is created by the hydrogen atoms of glycine-193 and serine-195 which stabilizes the negative charge on the carbonyl oxygen atom of the cleaved amides. The aspartate in the catalytic pocket is responsible for the specificity of attracting and stabilizing positively charged lysine/arginine. Therefore trypsin cleaves proteins at the C-terminal side of the amino acids. This occurs within the polypeptide chain.

There is a nucleophilic attack by the hydroxyl group from serine-195 on the carbonyl carbon of the substrate while the histidine stabilizes the serine with a hydrogen bond between a nitrogen and the hydroxyl hydrogen. This creates a tetrahedral intermediate. Next an electron pair from the carbonyl oxygen forms a double bond and the hydrogen bonds to the polypetide change leaving the histidine, which cleaves the chain. Next the oxygen of a water molecule performs a nucleophilic attack on the cabonyl carbon where the electrons shift to the oxygen, removing the double bond. This is again stabilized by histidine and creates a second tetrahedral intermediate. The electron pair from the oxygen creates a double bond while the serine-polypetide chain is cleaved back into the original serine and histidine molecules with the polypeptide chain now cleaved into two halves.